1. Field of the Invention
The present invention relates to a surface-capacitive type touch sensor device and an electronic apparatus and the like having the same.
2. Description of the Related Art
The touch sensor device is a device which detects coordinates of a position pointed by using a finger, a pen, or the like, or detects occurrence of pointing actions. Normally, it is used in combination with a surface display device such as a liquid crystal display (referred to as LCD hereinafter) or a plasma display panel (referred to as PDP hereinafter).
A man-to-machine interface can be achieved by inputting an output of a touch sensor device to a computer, and controlling the display contents of a display device by the computer or by controlling an appliance, for example. Currently, the touch sensor devices are broadly used in daily lives such as with game machines, portable information terminals, ticketing machines, ATMs (Automated Teller Machines), car navigation systems, and the like. In accordance with improvements in the performance of computers and spread of network connecting environments, services provided with electronic apparatuses have been diversified. Accordingly, there are more and more increasing demands for display devices having the touch sensor device.
As types of the touch sensor devices, known are a capacitive type, a resistance film type, an infrared type, an ultrasonic type, an electromagnetic induction type, and the like. Among the touch sensor devices, the capacitive-type touch sensor device can detect touches of fingers through glass and plastics in various thicknesses, thereby exhibiting solid quality in many application fields such as in industrial products, white goods, and the like. Note, however, that the items used for touching the sensor are limited to fingers and electrostatic conductive items forming a capacitance equivalent to the fingers.
The capacitive-type touch sensor device is further classified into a projected capacitive type and a surface capacitive type.
The projected capacitive type is a type which is formed by disposing X-Y transparent electrodes in matrix. When a finger approaches to the X-Y transparent electrodes, the capacitance between the electrodes increases. A controller detects the change in the capacitance on the X-Y line, and detects the position of the finger.
In the meantime, the projected capacitive type has XY electrodes on both sides of a glass substrate. In order to form the transparent electrodes on both sides of the glass substrate, it is necessary to deposit two layers of transparent conductive layers. In addition, it is necessary to pattern the conductive transparent layers for forming the transparent electrodes in a matrix form, which requires a large number of manufacturing steps. Further, in addition to having a large number of XY electrodes, terminals corresponding to each of the XY electrodes are required. Thus, the number of terminals becomes great as well.
Further, a typical material for transparent electrodes is ITO (indium tin oxide). Because of expansion in the liquid crystal panel and touch panel markets, there have been increasing demands for ITO. In particular, indium that constitutes ITO is a rare metal, which is expensive. Further, ITO is formed by vapor deposition, so that a long manufacturing tact time is required. Thus, it is not possible to be mass-produced. Therefore, ITO film makers cannot increase enough production of the films, and there is a short-supply of ITO films. This results in increasing the price for members of transparent electrodes. As a result, the manufacturing cost of the projected capacitive type is increased.
In the meantime, the surface type simply needs to form one layer of transparent conductive layer on the surface of an insulating substrate as described later, so that the structure is simpler and the manufacturing cost can be suppressed compared to the case of the projected capacitive type.
That is, a typical surface type is formed with an insulating substrate, a uniform transparent conductive layer formed on the surface thereof, and a thin insulating layer (protective layer) formed on the top surface thereof. When driving the touch sensor device, an AC voltage is applied to the four corners of the transparent conductive layer. When a finger touches the touch sensor, a small current flows to the finger via a capacitance formed between the transparent conductive layer and the finger. This current flows to the point touched by the finger (the point contacted by the finger) from each of the four corners of the transparent conductive layer. Then, a signal processing circuit detects occurrence of the touch from the sum of each of the currents. Further, the signal processing circuit calculates coordinates of the touched position from the ratio of each of the currents. For example, the techniques regarding such surface type are disclosed in U.S. Pat. No. 4,293,734 (Patent Document 1), Japanese Patent Application Publication Sho 56-500230 (Patent Document 2), Japanese Unexamined Patent Publication 2001-099609 (Patent Document 3), Japanese Unexamined Patent Publication 2005-269090 (Patent Document 4), Japanese Unexamined Patent Publication 2007-264923 (Patent Document 5), and Japanese Patent No. 3864512 (Patent Document 6).
However, there are following issues with the surface-capacitive type touch sensor device.
In a case where a surface-capacitive type touch sensor device is mounted to a portable device, i.e., under a mobile environment, deterioration in S/N (signal-to-noise ratio) of a touch sensor function for detecting the contact positions results in degradation in the sensitivity and positioning accuracy of the touch sensor function. Further, the contact sensitivity and position detecting accuracy are susceptible to changes in the surrounding environments.
It is therefore an exemplary object of the present invention to provide a touch sensor device and the like capable of improving the position detecting accuracy of a surface-capacitive type touch sensor device.